1. Field of the Invention
The present invention relates to an information recording apparatus and method for recording information on an information recording medium such as an optical disc.
2. Related Background Art
In a conventional information recording apparatus (to be simply referred to as a disc apparatus hereinafter), the following access control is executed to achieve a high-speed read operation. That is, data read out from a disc is temporarily stored in a cache memory. When the same data is accessed in the next read operation, data stored in the memory is transferred without accessing to the disc. Also, data written in the disc apparatus is stored in the cache memory to achieve high-speed data transfer. When such a cache memory is used, the disc apparatus has information of data stored in the cache memory, i.e., a table for managing the cache. Upon input/output of data, data access control is executed by looking up this management table.
As a write method using a cache memory, several methods such as a write-through method, a write-back method, and the like are known. In the write-through method, when a certain file (data) is written in a disc in response to a command from a host computer, the file is stored in a cache memory, and is simultaneously written in the disc. In the write-back method, when data from a host computer is stored in a cache memory, the completion of the write access is notified to the host computer, thereby shortening the write time.
Also, the following method (delay write) is known. In this method, the notification of write completion is made to a host computer upon storage of data in a cache memory as in the write-back method, but data write in a disc begins when the disc apparatus is disconnected from the host computer. Also, in terms of the data input/output relationship between the host computer and the disc apparatus, it is known that most data input/output requests from the host computer are those (sequential accesses) for a portion with continuous addresses assigned to the disc.
A conventional sequential write operation will be described below with reference to FIGS. 1 and 2. FIG. 1 is a plan view showing the recording surface of a magneto-optical disc. On the magneto-optical disc shown in FIG. 1, spiral tracks are formed, and one track is constituted by 16 sectors.
FIG. 2 is a chart showing the time sequence of the state of an interface bus between the host computer and a drive apparatus and the access state to a disc in the drive apparatus. A case will be explained below wherein the host computer issues write request 1 from sector 0 to sector 3 on a track n, and write request 2 from sector 4 to sector 7 thereof to the drive apparatus. At time t.sub.1, the host computer starts data transfer of write request 1, and at the same time, the drive apparatus performs a seek operation for moving the recording/reproduction head to sector 9 on the target track n. At time t.sub.2, the head reaches sector 0 on the track n in FIG. 1, and starts recording. Upon completion of recording up to sector 3 at time t.sub.3, notification 1 of write completion is sent back to the host computer.
The host computer subsequently transfers data of write request 2 from sector 4 to sector 7 on the track n in FIG. 1. However, at this time, since the recording/reproduction head of the drive apparatus has already passed the sector 4, the recording/reproduction head 1 must be moved to a position one track before so as to execute write request 2. For this purpose, the drive apparatus waits for rotation of the disc, and starts recording at time t.sub.4. Upon completion of recording at time t.sub.5, notification 2 of write completion is sent back to the host computer.
However, in the conventional write method, when sequential write requests are issued to the disc apparatus, the notification of write completion is sent back to the host computer after each body of data is recorded on a disc. For this reason, when the next continuous data is to be recorded on the disc, the disc apparatus must wait for rotation of the disc. For this reason, when a continuous portion is to be recorded, a very long write time is required. In the conventional write-through method, data is written in both the cache memory and the disc, and upon completion of both write operations, the notification of write completion is sent back to the host computer. For this reason, the actual write time is substantially equal to that in a method using no disc cache. Thus, the high-speed characteristics of the cache memory are not utilized.
Furthermore, in the write-back method, although high-speed data transfer is attained using the cache memory, no special means for sequential write requests is adopted, and each write processing must be performed after given rotation wait time. The write-back method must have management information (e.g., request addresses, cache memory addresses, capacity, and the like) of data stored in the cache memory, and must search for and update the management information upon execution of new write processing. In addition, since the write-back method processes data with an arbitrary length at arbitrary addresses, buffer management is complicated. As a result, the search processing time for determining whether or not a request block is stored in the cache buffer in response to a write command, and the processing time for updating management information after the write processing (e.g., detection of the written block) are undesirably prolonged. Furthermore, since read processing, which is not related to the write-back method, requires search processing for determining whether or not a request block is stored in the cache buffer, the search processing time is directly added as an overhead of a command if a cache hit does not occur, thus delaying the command execution time.